U.S. patent number 10,808,970 [Application Number 15/762,420] was granted by the patent office on 2020-10-20 for ionic liquid-based absorption cooling system with high coefficient of performance.
This patent grant is currently assigned to University of Florida Research Foundation, Incorporated, University of Notre Dame. The grantee listed for this patent is University of Florida Research Foundation, Incorporated, University of Notre Dame. Invention is credited to Edward Maginn, Saeed Moghaddam, Abhilash Paneri.
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United States Patent |
10,808,970 |
Moghaddam , et al. |
October 20, 2020 |
Ionic liquid-based absorption cooling system with high coefficient
of performance
Abstract
An absorption refrigeration system (ARS), includes a
sorbent-refrigerant pair that has an ionic liquid (IL) sorbent and
a refrigerant that displays a lower critical lower critical
solution temperature (LCST) at a temperature of 50 to 100.degree.
C., wherein the separation of the sorbent from the refrigerant
occurs upon heating the sorbent-refrigerant pair to a temperature
above the LCST. This liquid-liquid phase separation requires
significantly less energy to desorb the refrigerant from the
sorbent than vapor-liquid phase separation in traditional ABSs.
Inventors: |
Moghaddam; Saeed (Gainesville,
FL), Paneri; Abhilash (Tigard, OR), Maginn; Edward
(South Bend, IN) |
Applicant: |
Name |
City |
State |
Country |
Type |
University of Florida Research Foundation, Incorporated
University of Notre Dame |
Gainesville
South Bend |
FL
IN |
US
US |
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Assignee: |
University of Florida Research
Foundation, Incorporated (Gainesville, FL)
University of Notre Dame (South Bend, IN)
|
Family
ID: |
1000005130181 |
Appl.
No.: |
15/762,420 |
Filed: |
September 27, 2016 |
PCT
Filed: |
September 27, 2016 |
PCT No.: |
PCT/US2016/053881 |
371(c)(1),(2),(4) Date: |
March 22, 2018 |
PCT
Pub. No.: |
WO2017/058747 |
PCT
Pub. Date: |
April 06, 2017 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20180259229 A1 |
Sep 13, 2018 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62233536 |
Sep 28, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K
5/047 (20130101); F25B 15/02 (20130101); F25B
15/06 (20130101); Y02A 30/27 (20180101); Y02B
30/62 (20130101); Y02P 20/10 (20151101) |
Current International
Class: |
F25B
15/02 (20060101); F25B 15/06 (20060101); C09K
5/04 (20060101) |
Field of
Search: |
;252/67 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO 2007/070607 |
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Jun 2007 |
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WO |
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WO-2014082420 |
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Jun 2014 |
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WO |
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WO 2015/103199 |
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Jul 2015 |
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WO |
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Other References
"Lithium bis(trifluoromethylsulfonyl)imide", Matrix Scientific, VWR
International, LLC, 2020. (Year: 2020). cited by examiner .
Dittmar, Harro R., et al., "Lower Critical Solution Temperature in
the Metastable Region of an Ionic Solution in a Non-Polar Solvent",
J. Phys. Chem. B, 2009, 113 (5), pp. 1249-1252, American Chemical
Society. cited by applicant .
Fukumoto, Kenta, et al., "LCST-Type Phase Changes of a Mixture of
Water and Ionic Liquids Derived from Amino Acids", Angew. Chem.,
2007, 119, pp. 1884-1887, Wiley-VCH Verlag GmbH & Co. KGaA.
cited by applicant .
Kohno, Yuki, et al., "Material design of ionic liquids to show
temperature-sensitive LCST-type phase transition after mixing with
water", Australian Journal of Chemistry, 2011, 64(12), pp.
1560-1567, CSIRO Publishing. cited by applicant .
Lachwa, Joanna, et al., "Evidence for Lower Critical Solution
Behavior in Ionic Liquid Solutions", J. Am. Chem. Soc., 2005, 127
(18), pp. 6542-6543, American Chemical Society. cited by applicant
.
Costa, Anabela, J.L., et al., "Unusual LCST-Type Behaviour Found in
Binary Mixtures of Choline-Based Ionic Liquids with Ethers", RSC
Advances, 2013, 3, pp. 10262-10271, The Royal Society of Chemistry,
RSC Publishing. cited by applicant .
International Searching Authority, International Search Report for
Application No. PCT/US2016/053881, dated Dec. 8, 2016, 3 pages,
Korean Intellectual Property Office, Republic of Korea. cited by
applicant.
|
Primary Examiner: McGinty; Douglas J
Attorney, Agent or Firm: Alston & Bird LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is the U.S. national stage application of
International patent application No. PCT/US2016/053881, filed Sep.
27, 2016, which claims the benefit of U.S. Provisional Application
Ser. No. 62/233,536, filed Sep. 28, 2015, the disclosures of which
are hereby incorporated by reference in their entireties, including
all figures, tables and drawings.
Claims
We claim:
1. An absorption refrigeration system (ARS), comprising: a
sorbent-refrigerant pair, the sorbent-refrigerant pair comprising
one or more ionic liquids (ILs) comprising at least: an anion
selected from a group consisting of
bis(trifluoromethanesulfonyl)imide ([Tf.sub.2N].sup.-), SbF.sub.6,
B(C.sub.6H.sub.3).sub.4.sup.-, SO.sub.3F.sup.-, and
CHB.sub.11F.sub.11, and a cation selected from among a group
consisting of hydroxyl functionalized tetraalkyl ammonium cations,
hydroxyl functionalized tetraalkyl phosphonium cations,
dialkylimidazolium cations, trialkylimidazolium cations,
tetraalkylammonium cations, tetraalkylphosphonium cations,
N,N-dialkylpyrrolidinium cations, and combinations thereof; and a
liquid-liquid separator, wherein the sorbent-refrigerant pair
undergoes a lower critical solution temperature (LCST) at a
temperature of between 30.degree. C. and 200.degree. C.
2. The absorption refrigeration system (ARS) according to claim 1,
wherein the hydroxyl functionalized tetraalkyl ammonium cations,
are [N.sub.x y z wOH].sup.+ cations where x, y, and z are
independently C.sub.1 to C.sub.12 alkyl, and wOH is a C.sub.2 to
C.sub.12 hydroxyalkyl group with w hydroxyl groups.
3. The absorption refrigeration system (ARS) according to claim 2,
wherein wOH is 2OH.
4. The absorption refrigeration system (ARS) according to claim 1,
wherein the hydroxyl functionalized tetraalkyl phosphonium cations,
are [P.sub.x y z wOH].sup.+ cations where x, y, and z are
independently C.sub.1 to C.sub.12 alkyl, and wOH is a C.sub.2 to
C.sub.12 hydroxyalkyl group with w hydroxyl groups.
5. The absorption refrigeration system (ARS) according to claim 1,
wherein the dialkylimidazolium cations and trialkylimiazolium
cations are selected from 1-butyl-3-methylimidazolium
([bmim].sup.+), 1-ethyl-3-methylimidazolium ([emim].sup.+),
2,3-dimethyl-1-ethylimidazolium ([emmim].sup.+) and
2,3-dimethyl-1-propylimidazolium ([pmmim].sup.+).
6. The absorption refrigeration system (ARS) according to claim 1,
wherein the ILs are the tetraalkylammonium cations, the
tetraalkylphosphonium cations, and/or the N,N-dialkylpyrrolidinium
cations, wherein the alkyls are independently C.sub.1 to C.sub.12
alkyl and wherein the alkyls can be interrupted one or more times
by oxygens.
7. The absorption refrigeration system (ARS) according to claim 1,
wherein the refrigerant is water, an alcohol, or an ether.
8. The absorption refrigeration system (ARS) according to claim 7,
wherein the alcohol is selected from methanol, ethanol, n-propanol,
i-propanol, cyclopropanol, n-butanol, sec-butanol, i-butanol,
t-butanol, cyclobutanol, any methyl substituted propanol, any
pentanol, cyclopentanol, any methyl substituted butanol, any
dimethyl substituted propanol, any ethyl substituted propanol, any
hexanol, cyclohexanol, any methyl substituted cyclopentanol, any
dimethyl substituted cyclobutanol, any ethyl substituted
cyclobutanol, any trimethyl substituted propanol, any methyl,ethyl
substituted propanol, or any propyl substituted propanol.
9. The absorption refrigeration system (ARS) according to claim 7,
wherein the ether is selected from diethyl ether, di-n-propyl
ether, di-i-propyl ether, methyl-propyl ether, ethyl-propyl ether,
tetrahydrofuran, and tetrahydropyran.
10. The absorption refrigeration system (ARS) according to claim 1,
wherein the LCST between 50.degree. and 100.degree. C.
11. An absorption refrigeration system (ARS), comprising a
sorbent-refrigerant pair and a liquid-liquid separator, wherein the
sorbent-refrigerant pair comprises at least one ionic liquid (IL)
and undergoes a lower critical solution temperature (LCST) at a
temperature between 30.degree. C. and 200.degree. C., wherein the
at least one IL comprises one or more dialkylimidazolium cations
and one or more non-nucleophilic hexafluorophosphate anions.
12. The absorption refrigeration system (ARS) according to claim
11, wherein the at least one IL further comprises one of hydroxyl
functionalized tetraalkyl ammonium cations, hydroxyl functionalized
tetraalkyl phosphonium cations, trialkylimidazolium cations,
tetraalkylammonium cations, tetraalkylphosphonium cations,
N,N-dialkylpyrrolidinium cations, and combinations thereof.
13. The absorption refrigeration system (ARS) according to claim
12, wherein the hydroxyl functionalized tetraalkyl ammonium
cations, are [N .sub.x y z wOH].sup.+ cations where x, y, and z are
independently C.sub.1 to C.sub.12 alkyl, and wOH is a C.sub.2 to
C.sub.12 hydroxyalkyl group with w hydroxyl groups.
14. The absorption refrigeration system (ARS) according to claim
13, wherein wOH is 2OH.
15. The absorption refrigeration system (ARS) according to claim
12, wherein the dialkylimidazolium cations and trialkylimiazolium
cations are selected from 1-butyl-3-methylimidazolium
([bmim].sup.+), 1-ethyl-3-methylimidazolium ([emim].sup.+),
2,3-dimethyl-1-ethylimidazolium ([emmim].sup.+) and
2,3-dimethyl-1-propylimidazolium ([pmmim].sup.+).
16. The absorption refrigeration system (ARS) according to claim
11, wherein the refrigerant is water or an alcohol selected from
methanol, ethanol, n-propanol, i-propanol, cyclopropanol,
n-butanol, sec-butanol, i-butanol, t-butanol, cyclobutanol, any
methyl substituted propanol, any pentanol, cyclopentanol, any
methyl substituted butanol, any dimethyl substituted propanol, any
ethyl substituted propanol, any hexanol, cyclohexanol, any methyl
substituted cyclopentanol, any dimethyl substituted cyclobutanol,
any ethyl substituted cyclobutanol, any trimethyl substituted
propanol, any methyl,ethyl substituted propanol, or any propyl
substituted propanol.
17. An absorption refrigeration system (ARS), comprising a
sorbent-refrigerant pair and a liquid-liquid separator, wherein the
sorbent-refrigerant pair comprises at least one ionic liquid (IL)
and undergoes a lower critical solution temperature (LCST) at a
temperature between 30.degree. C. and 200.degree. C., wherein the
at least one IL comprises one or more alkylimidazolium cations and
one or more non-nucleophilic hexafluorophosphate anions, and
wherein the refrigerant comprises an alcohol or water.
18. The absorption refrigeration system (ARS) of claim 17, wherein
the alkylimidazolium cation is selected from
1-butyl-3-methylimidazolium ([bmim].sup.+),
1-ethyl-3-methylimidazolium ([emim].sup.+),
2,3-dimethyl-1-ethylimidazolium ([emmim].sup.+) and
2,3-dimethyl-1-propylimidazolium ([pmmim].sup.+).
19. The absorption refrigeration system (ARS) of claim 17, wherein
the at least one IL further comprises hydroxyl functionalized
tetraalkyl phosphonium cations, trialkylimidazolium cations,
tetraalkylammonium cations, tetraalkylphosphonium cations,
N,N-dialkylpyrrolidinium cations, and combinations thereof.
Description
BACKGROUND OF INVENTION
Absorption refrigeration systems (ARSs) have the potential to play
a significant role in our future energy economy if high
performance, compact, and robust systems are developed. Compact
ARSs are possible; however, the fundamental thermodynamics of the
cycle and hence the coefficient of performance (COP) of absorption
systems have not significantly improved since their introduction in
the 18th century. The performance is primarily limited because of
energy required for desorbing refrigerant from the working fluids.
State of the art systems employ, for example, a LiBr-water working
fluid that is concentrated in the desorber by evaporating the
refrigerant, and the heat energy is provided to promote the phase
change from liquid water in solution to gaseous water vapor. The
state of the art ARSs can include one or more additional salts with
the LiBr to suppress crystallization of LiBr after desorption, or
use an alternate salt that does not readily crystallize in the
system, for example, as disclosed in Atkins, U.S. Pat. No.
5,846,450.
Recently, the use of ionic liquids in ARSs has been disclosed,
where the ionic liquid is used as a crystallization suppressing
additive to the sorbent, as disclosed in Shiflett et al. US Patent
Application Publication No. 2012/0011886. In general, the ionic
liquids employed as the sorbent and the refrigerant and sorbent are
employed in the traditional manner, where heating separates the
refrigerant as a gas from the sorbent. As taught in Shiflett et al.
US Patent Application Publication No. 2010/0132384, systems are
constructed to maintain a single liquid phase and not promote the
formation of separated liquid phases by maintaining a working
temperature that remain above any upper critical solution
temperature.
Jork et al. U.S. Pat. No. 8,069,687 teaches an ARS including a
separator wherein a liquid-liquid phase separation of the working
medium is performed. The one liquid phase has the sorbent at a
concentration of at least 20% by weight and a second liquid phase
having a refrigerant concentration of at least 20% by weight. The
working medium is one phase residing in a liquid-liquid miscibility
gap which upon heating or cooling is at a temperature that is
outside of an upper or lower critical solution temperature. By
changing the desorption process to have refrigerant undergo a
liquid-liquid separating from the sorbent at a moderate
temperature, a significant reduction of the system's energy input
can permit significant increases in the efficiency of a compact
ARS. The sorbent is an ionic liquid having alkyl and aryl
tosylates, fluoroalkyl tosylates, nitrate, sulfate,
hydrogensulfate, alkyl and aryl sulfates, polyether sulfates and
polyethersulfonates, fluoroalkyl sulfates, alkyl and
arylsulfonates, fluorinated alkyl and arylsulfonates, alkyl and
aryl carboxylates, fluoroalkyl carboxylates, cyanate, polyether
phosphates and dicyanamide anion. The refrigerant is taught to be
water, ammonia, methylamine, dimethylamine, halogenated
hydrocarbons, 2,2,2-trifluroethanol, or methanol. However, there is
not a single sorbent-refrigerant pair identified that necessarily
permits the use of the liquid-liquid separator even though the
temperature range recited for the separation is anywhere from -50
to 250.degree. C., where this phase separation is taught to occur
at either a lower critical solution temperature (LCST) or a upper
critical solution temperature (UCST).
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows a generalized T-x diagram for a sorbent-refrigerant
pair that displays a lower critical solution temperature (LCST)
that can be used in an absorption refrigeration system (ARS),
according to an embodiment of the invention.
FIG. 2 is a schematic drawing of an ARS employing a separator,
according to an embodiment of the invention.
FIG. 3 shows photographs of a [bmim].sup.+[BF.sub.4].sup.- and
n-butanol IL refrigerant pair that undergoes conversion from a
homogeneous solution (top) through a cloud point (center) to a
phase separated (bottom) n-butanol top layer and an IL bottom
layer.
FIG. 4 shows plots of computed isotherms for
[C.sub.2mim].sup.+[Tf.sub.2N].sup.- with methanol and ethanol.
FIG. 5 shows the structure of the ionic liquid,
tetra-nbutylphosphonium trifluoromethanesulfonyl leucine
([P4444].sup.+[Tf-Leu].sup.-) which displays a LCST with water,
according to an embodiment of the invention.
Other objects, features, and advantages of the invention will be
apparent to those skilled in the art from the detailed description
of the invention which will now follow, taken in conjunction with
the tables, drawings, and the accompanying claims.
DETAILED DISCLOSURE
Embodiments of the invention are directed to an absorption
refrigeration system (ARS) and absorption refrigeration process
where the sorbent, or absorbent) is an ionic liquid (IL) that phase
separates from a refrigerant, or absorbate, in a liquid-liquid
separator at a lower critical solution temperature (LCST) is
employed rather than a desorber, which improves the coefficient of
performance (COP). As no phase change is involved in separation,
the energy required for vaporizing the refrigerant to permit its
subsequent absorption in the concentrated IL sorbent is drastically
reduced. The LCST results in phase separation upon heating, as
illustrated in FIG. 1. The LCST temperature depends upon the
molecular structure of the IL and the refrigerant, and can be about
30 to about 200.degree. C., according to an embodiment of the
invention. In an embodiment of the invention, the LCST is about
50-60.degree. C. while the absorber temperature is at least
5.degree. C. below the LCST such that a homogeneous
sorbent-refrigerant solution forms upon absorption of the
refrigerant. The refrigerant, also referred to as the absorbate, is
a compound or mixture of compounds that undergoes phase changes
between a liquid and gaseous state upon heating and cooling. The
sorbent, also referred to as the absorbent, is a non-volatile IL or
a mixture of an IL with other non-volatile components that absorbs
the absorbate in the absorber portion of an ARS, as illustrated in
FIG. 2.
For an ARS, according to an embodiment of the invention, the
sorbant-refrigerant pair has good miscibility at the absorber
temperature and readily phase separates with minimal heating to
yield two liquid phases in the separator. Cholinium cation,
2-hydroxyethyl)trimethylammonium, and cholinium-like cations allow
ILs that associate with ether refrigerants to display LCST behavior
for the desired temperature window for ARSs, according to an
embodiment of the invention. Cholinium-like cations are hydroxyl
functionalized tetraalkyl ammonium cations, which can be indicated
as [N.sub.x y z wOH].sup.+ where x, y, and z are independently
C.sub.1 to C.sub.12 alkyl, and wOH is a C.sub.2 to C.sub.12
hydroxyalkyl group, for example, 2OH represents the 2-hydroxyethyl
group. Salts containing these cations are usually coupled with
non-nucleophilic anions, such as, but not limited to,
bis(trifluoromethanesulfonyl)imide ([Tf.sub.2N].sup.-) that display
a melting point, that is less than any temperature experienced
within the ARS. Other non-nucleophilic anion include, but are not
limited to, Cl.sup.-, Br.sup.-, I.sup.-, BF.sub.4.sup.-,
SbF.sub.6.sup.-, B(C.sub.6H.sub.5).sub.4.sup.-, PF.sub.6.sup.-,
SO.sub.3F.sup.-, CHB.sub.11F.sub.11.sup.-, HCO.sub.2.sup.-,
CH.sub.3CO.sub.2.sup.-, HSO.sub.4.sup.-: CH.sub.3OSO.sub.3.sup.-:
C.sub.2H.sub.5OSO.sub.3.sup.-, AlCl.sub.4.sup.-, CO.sub.3.sup.2-,
HCO.sub.3.sup.-, NO.sub.2.sup.-: SO.sub.4.sup.2-, PO.sub.3.sup.2-,
HPO.sub.3.sup.2-, H.sub.2PO.sub.3.sup.-, PO.sub.4.sup.3-,
HPO.sub.4.sup.2-, H.sub.2PO.sub.4.sup.-, HSO.sub.3.sup.-,
CuCl.sub.2.sup.-, [BR.sup.1R.sup.2R.sup.3R.sup.4].sup.-, and
[BOR.sup.1OR.sup.2OR.sup.3OR.sup.4].sup.-, where R.sup.1, R.sup.2,
R.sup.3, and R.sup.4 are alkyl or substituted alkyl. In an
embodiment of the invention, the melting point of the sorbant is
depressed as a mixture of different cholinium salts, having either
different cations, anions, or both. In addition to cholinium-like
cations, ILs, according to embodiments of the invention include,
but are not limited to: hydroxyl functionalized tetraalkyl
phosphonium cations which can be indicated as [P.sub.x y z
wOH].sup.+ where x, y, and z are independently C.sub.1 to C.sub.12
alkyl, and wOH is a C.sub.2 to C.sub.12 hydroxyalkyl group;
dialkylimidazolium cations and trialkylimidazolium cations, where
the alkyls are independently C.sub.1 to C.sub.12 alkyl;
tetraalkylammonium cations, where the alkyls are independently
C.sub.1 to C.sub.12 alkyl; tetraalkylphosphonium cations, where the
alkyls are independently C.sub.1 to C.sub.12 alkyl; and/or
N,N-dialkylpyrrolidinium cations, where the alkyls are
independently C.sub.1 to C.sub.12 alkyl. For these IL cations, one
or more of the alkyl groups can be substituted with one or more
hydroxyl groups or the alkyl chain can be interrupted with one or
more oxygen atoms. The alkyl groups can be linear, branched,
plurally branched, or cyclic, wherein the cycloalkane can be
substituted with an alkyl group, a hydroxyl group, or be
interrupted with one or more oxygen atoms. Hydroxyl groups, for
example, those of the cholinium cation, allow formation of hydrogen
bonds with the oxygen of an ether or alcohol refrigerant, or water,
resulting in miscibility of the sorbent-refrigerant pair. Upon
heating to a temperature in excess of the LCST, the hydrogen
bonding between hydroxyl groups of the cholinium-like salts and,
for example, the ether is insufficient to overcome the ionic and
hydrogen bonding association between cholinium-like salts. The LCST
depends on the structure of the alkyl substituents of the
tetraalkyl ammonium cations, the anions, and the refrigerant.
Consequently, an ionic liquid can be designed to have a specific
LCST with a specific refrigerant.
So that one can appreciate the efficiency improvement available by
the implementation of an IL and refrigerant where the LCST is
between 50 and 200.degree. C. and allow phase separation at these
temperatures, computations for a model for a hypothetical
[P.sub.4444].sup.+[Tf-Leu].sup.--water pair that allows separation
at 172.degree. C. and generates an evaporator temperature of
5.degree. C. have been carried out. Upon solving the equations for
conservation of mass and energy in the cycle, values are generated,
as tabulated in Table 1, below, suggests that a COP.sub.primary of
5.8 can be achieved for a 3 ton system. Such a value implies that
the primary energy consumption for air-conditioning can be reduced
by an order of magnitude.
TABLE-US-00001 TABLE 1 Input Parameters and Calculated Values for
an ABS Employing an IL-Refrigerant Pair Parameter Value Evaporator
temperature 5.degree. C. Separator temperature 172.degree. C.
Cooling capacity 10.6 kW Separator heat input 1.86 kW Solution HX
effectiveness 0.8 COP.sub.primary 5.8
Particularly, where the IL-refrigerant cycle employing a separator
is used with high efficiency membrane-based absorption technology,
very high COP.sub.primay values can be achieved. Membrane-based
absorbers and desorbers are disclosed in Moghaddam et al., "3D
Microstructures for Rapid Absorption/Desorption in Mechanically
Constrained Liquid Absorbents" PCT Application No.
PCT/US2014/072664 filed Dec. 30, 2014, which is incorporated by
reference,
In another embodiment of the invention, the IL sorbent has a
dialkylimidazolium cation and a non-nucleophilic anion with a
refrigerant that is a C.sub.1 to C.sub.6 alcohol, for example,
1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
([bmim].sup.+[Tf.sub.2N].sup.-) and the refrigerant is n-butanol,
where the LCST is about 52.degree. C. As shown in FIG. 3, the
[bmim].sup.+[Tf.sub.2N].sup.- butanol pair readily converts to a
homogeneous solution at temperatures below the LCST, goes through a
cloud point where phase separation occurs that clearly exists as
two nearly immiscible phases at temperatures in excess of the LCST.
The alcohols employed as refrigerant include, but are not limited
to, methanol, ethanol, n-propanol, i-propanol, cyclopropanol,
n-butanol, sec-butanol, i-butanol, t-butanol, cyclobutanol, any
methyl substituted propanol, any pentanol, cyclopentanol, any
methyl substituted butanol, any dimethyl substituted propanol, any
ethyl substituted propanol, any hexanol, cyclohexanol, any methyl
substituted cyclopentanol, any dimethyl substituted cyclobutanol,
any ethyl substituted cyclobutanol, any trimethyl substituted
propanol, any methyl, ethyl substituted propanol, or any propyl
substituted propanol. The refrigerant can be water. Refrigerants
can be ethers, including, but not limited to, diethyl ether,
di-n-propyl ether, di-i-propyl ether, methyl-propyl ether,
ethyl-propyl ether, tetrahydrofuran, and tetrahydropyran.
The cycle consists of a separator, as shown in FIG. 2 in which the
refrigerant-absorbent mixture after heating above the LCST separate
into two liquid fluids. The refrigerant then flows into the
evaporator, through an expansion valve, where it evaporates with
the removal of heat from the ambient to create cooling. The
evaporated refrigerant then flows into the absorber. A heat
exchanger recovers significant portion of the absorbent's thermal
energy before it enters the absorber. Upon arriving in the
absorber, the absorbent absorbs the incoming refrigerant vapor from
the evaporator. The latent heat of refrigerant released into the
absorbent and the excess enthalpy are dissipated into the ambient.
The mixture exits the absorber as a single-phase solution which is
passed through a heat exchanger where, upon heating, the working
pair enters the separator as two liquid phases and the cycle
repeats.
To identify appropriate IL-refrigerant working pairs, known room
temperature ILs are modeled using a molecular Gibbs ensemble Monte
Carlo simulation for candidate IL-refrigerant pairs in order to
predict the key thermodynamic properties. These properties are
correlated to the molecular structure and energetics of the system
and constitute a rational design strategy for identification of
working pairs. FIG. 4 shows computed isotherms for methanol and
ethanol in 1-ethyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)amide ([emim].sup.+[Tf.sub.2N].sup.-),
where the simulations agree very well with experimental
measurements. In addition to computing isotherms, the simulations
allow us to determine the enthalpy of solution and heat capacity.
Candidate ILs are disclosed in Crosthwaite et al., J. Phys. Chem.
B, 2004, 108, 5113-9, Domanska et al., J. Chem. Eng. Data, 2010,
55, 773-7, Lachwa et al., J. Am. Chem. Soc., 2005, 127, 6542-3,
Fukumoto et al., Angew. Chemie., 2007, 119, 1884-7, Dittmar et al.,
J. Phys. Chem. B., 2009, 113, 1249-52, Kohno et al., Aust. J.
Chem., 2011, 64, pp. 1560-7, Costa et al., RSC, 2013, 10262-71,
which are incorporated by reference herein.
In an embodiment of the invention, the IL-refrigerant pair is
tetra-nbutylphosphonium trifluoromethanesulfonyl leucine
([P.sub.4444].sup.+[Tf-Leu].sup.-) mixed with water. In an
embodiment of the invention, the IL is
N-alkyl-N,N-dimethylhydroxyethylammoniumbis(trifluoromethane)
sulfonylimide mixed with ethers.
All patents, patent applications, and publications referred to or
cited herein are incorporated by reference in their entirety,
including all figures and tables, to the extent they are not
inconsistent with the explicit teachings of this specification.
It should be understood that the examples and embodiments described
herein are for illustrative purposes only and that various
modifications or changes in light thereof will be suggested to
persons skilled in the art and are to be included within the spirit
and purview of this application.
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